NL192891C - Voltage control circuit with protection against transients. - Google Patents

Description

1 192891

Voltage control circuit with protection against transients

The invention relates to a voltage control circuit comprising a first and a second opposite conductor type transistor, which are connected in series with their coliector emitter circuit between a voltage source and a controlled output; a zener diode; a first base driving circuit for supplying a base voltage to the base of the first transistor connected to the output; and a second basic control circuit which is adapted to supply a basic voltage to the base of the second transistor connected to the voltage source and which comprises a pre-regulation circuit forming part of the first basic control circuit which receives a feedback signal from the controlled output .

A voltage control circuit of this kind is known from the article "Stabilisiertes Labor-Netzgerat für grossen Ausgangsspannungsbereich", D. Ulrich, Funkschav, part 42, no. 2.2 January 1970.

Electronic systems often have voltage regulators or control circuits that draw electric current at an uncontrolled supply voltage and which supply a regulated voltage to an electric load. In modern systems, many load circuits that require electrical power are integrated circuits. Integrated circuits and sensors used in conjunction with them require relatively low voltages, typically of six volts or less. It has become common in connection with these circuits and sensors to provide voltage control using integrated circuit voltage regulators that are powered on a separate chip or on the same chip as the integrated circuit.

Monolytically integrated circuits are increasingly used in motorized transport applications. The motorized transport environment imposes particularly strict voltage regulation requirements. Voltage transients of 80 or 90 volts of either polarity to ground may occur in the supply conductors due to the interaction of the alternator and the main voltage regulator, 25 when the engine is turned off or started quickly, or when a battery cable is removed or certain other electrical disconnected. In addition, motorized transport devices must be able to operate over a wide range of temperatures.

Therefore, a voltage regulator for many electronic circuits in the motorized transport applications must provide a relatively tightly regulated low voltage from the supply voltage which is subject to positive and negative voltage deviations many times the size of the controlled voltage. Furthermore, the voltage regulator must be able to provide such regulation or regulation over a wide temperature range. Ultimately, in motorized transport applications, cost and reliability are of great importance. Costs must be kept to a minimum, thus requiring a relatively simple circuit design that is easy to manufacture.

A problem encountered in circuits equipped with bipolar transistors is that such transistors, which may have voltage transients of the size expected in motorized transport applications, are difficult to fabricate using conventional monolytic integrated circuit manufacturing processes. Accordingly, integrated-40 circuit voltage regulators in motorized transport applications must have some form of protection against transient voltages. Various circuit designs and techniques for providing protection against transient voltages are known.

The object of the invention is to provide a voltage control circuit which is of a different type than the circuit known from the Ulrich article.

The voltage control circuit according to the invention is therefore characterized in that a current-limiting element is arranged in series with the series circuit of the two transistors; that a diode is present between a reference voltage and the junction of both transistors; that the two basic control circuits supply constant basic voltages during operation; and in that the first base driving circuit comprises the zener diode, which is included in the base circuit of the first transistor and which forward biasing circuit is set 50 by a biasing circuit forming part of the first basic driving circuit.

The voltage control circuit according to the invention has the advantage that it has a simple integrable construction. Furthermore, the voltage control circuit according to the invention is capable of controlling high interfering voltages of both polarities. Also, the voltage control circuit 55 of the invention provides a significantly increased breakdown limit for the entire voltage control circuit and voltage control up to the breakdown limit. In case of transistor breakdown, the current through the voltage control circuit is limited by internal impedances. Therefore, exceeding the 192891 2 transistor breakdown voltage will not necessarily result in destruction of the voltage control circuit.

It is noted that from US patent 3,428,820 a voltage control circuit is known comprising a first and a second transistor, each in the form of a Darlington pair. The base-5 voltage of one of the transistors is set using a zener diode. In addition, a resistor is arranged in series with the two transistors, as well as a diode between the junction of the two transistors and ground.

A preferred embodiment of the voltage control circuit according to the invention relates to a voltage control circuit, wherein the regulated voltage at the output is positive with respect to the reference voltage, the first transistor being of the NPN type and the second transistor of the PNP type, and wherein the emitter of the first transistor forms the output, characterized in that the current-limiting element is arranged between the emitter of the second transistor and the supply voltage source, and that the diode with its cathode at the junction of both transistors and with its anode at the reference voltage is connected. A circuit so characterized is further characterized in that the current limiting element is a P-type conductivity resistor which is diffused into an electrically insulated N-type conductivity well. The use of a resistor limits the current through the biasing transistor when it enters an electric breakdown state due to an excessive voltage of the second polarity. The selection of a diffused P-type conductivity resistor in an electrically insulated N-type conductivity well aims to further block transient voltages of the first polarity.

The invention will be further elucidated with reference to the drawing, in which figure 1 shows a diagram of a first embodiment of a voltage control circuit according to the invention; and Figure 2 shows a diagram of a second embodiment of a voltage control circuit according to the invention.

In Figure 1, an input terminal 11 is shown for recording an unregulated voltage which is subject to significant positive and negative voltage transients. This voltage is controlled and applied as a constant voltage to an output terminal 12. The control circuit is designed to be advantageously manufactured as a monolytically integrated circuit using conventional epitaxial manufacturing processes.

In the control circuit, the final control or regulation is obtained by means of a control pass transistor 13, which is indicated as an NPN transistor, the emitter of which is connected to the output terminal 12. The input terminal 11 is connected via a pre-control circuit 14 to the collector of the transistor 13. A constant voltage for the basic control of the transistor 13 is obtained by means of a zener diode 15, the cathode of which is connected to the base of the transistor and of which the anode is connected to ground or another reference potential source 16. The diode 15 is biased to breakdown by means of a biasing circuit 17. As will be explained in detail 40 below, both the pre-control circuit 14 and the bias circuit 17 are designed to prevent excessive positive and negative voltage transients from reaching the control pass transistor 13.

The pre-control circuit 14 has a PNP transistor 20 whose emitter is connected via a resistor 21 to the supply terminal 11 and whose collector is connected to the collector of the control-pass transistor 13. 45 For purposes to be explained below, resistor 21 is preferably a diffused resistor of P-type material in an electrically insulated N-type well. The junction of the collectors of the transistors 13 and 20 is connected to ground 16 via a diode 22 whose cathode is connected to the collector junction and whose anode is connected to earth. The base of the transistor 20 is connected to the drain of a field effect transistor (FET) 23 whose gate electrode has 50 ground 16 and whose source electrode is connected to the collector of an NPN transistor 24. Transistor 24 is connected to an NPN transistor 25 to form a current mirror. More specifically, the bases of transistors 24 and 25 are interconnected and the emitters of these transistors are connected to ground 16. The collector of the transistor 25 is connected to the bases of the transistors and through a resistor 26 to the output terminal 12. Of a field effect transistor 27, the drain electrode 55 is connected to the base of the transistor 20 and the source electrode and gate electrode are connected to ground 16.

In an actual embodiment, the bias circuit 14 was designed to limit the positive voltage on the collector of the control pass transistor 13 to approximately 34 volts, protecting this transistor 13 from excessive positive power transients. This clamping action is provided by the diode 22 wherein the transistor 20 serves to limit the current when the diode 22 trips. The transistor 20 and the resistor 21 limit the current when the supply voltage to ground is negative. More specifically, both transistor 20 and resistor 21 form biased diodes when subjected to a negative supply voltage. Therefore, neither the transistor nor the resistor will conduct current under these voltage polarity conditions.

The basic drive for the transistor 20 is obtained by means of the resistor 26 and the current mirror consisting of the transistors 24 and 25. The emitter current in the transistor 25 is determined by the regulated voltage at the output terminal 12 and the resistance value of the resistor 26. The transistors 24 and 25 are configured with suitable parameters to provide the emitter current with a desired multiple (e.g. 5 times) in the transistor 24 to increase. The collector current in the transistor 24 is supplied through the field effect transistor 23 to the base of the transistor 20. The field effect transistor 23 serves to limit the voltage to which the collector of the transistor 24 is subject to the transistor against the influence of large positive supply voltage transients. to protect.

The field effect transistor 27 ensures a sufficient base driving current for the transistor 20 to initiate the start of the control circuit.

The biasing circuit 17 provides a current sufficient to keep the zener diode 15 breakdown while protecting the base of the transistor 13 from excessive voltage transients. The biasing circuit contains a current mirror consisting of the PNP transistors 30 and 31, the emitters of which are connected to the supply terminal 11 via a resistor 32. Transistors 30 and 31 and resistor 32 block negative power transients in the same manner as transistor 20 and resistor 21. The collector of transistor 30 is connected to the drain electrodes of the field effect transistors 33 and 34 whose gate electrodes are connected to ground 16. The source electrode of the field effect transistor 33 is connected to the base of the NPN transistor 35 and the collector of an NPN transistor 36. The source electrode of the field effect transistor 34 is connected to the collector of the transistor 35. The emitter of the transistor 35 is connected directly to the base of transistor 36 and to ground 16 via a resistor 37. The emitter of transistor 36 is also connected to ground 16.

In operation, the collector current in transistor 30 is equal to the sum of the currents through the field effect transistors 33 and 34. The emitter current of transistor 30 is multiplied in transistor 31 by a predetermined factor (eg 4 times) and as bias current for the zener diode 15 is supplied. The portion of the collector current in the transistor 30 flowing through the field effect transistor 33 turns on the transistor 35, which conducts the current applied to the field effect transistor 34 through the resistor 37 to 16. The transistor 36 limits the collector current of the transistor 35 to a value determined by the base emitter voltage of the transistor 36 divided by the resistance value of the resistor 37. The current through the field effect transistor 33 is effectively limited by the characteristics of that device to the current it conducts when its gate and source electrodes are shorted. Therefore, a fixed current is supplied to the biasing diode 15. The field effect 40 transistor 34 serves to protect the transistor 35 from positive power transients. When the current through transistor 30 is tightly controlled, the current supplied to the cathode of diode 15 is also tightly controlled and the voltage at the base of transistor 13 is protected from the influences of positive and negative power transients.

In the embodiment of Figure 1 explained above, the zener diode 15 provides a voltage 45 reference to the forward transistor 13. In such a typical embodiment, the values of the circuit components were chosen to provide a controlled voltage of about 5.4 volts. In the circuit embodiment of Figure 2, a band interval reference is used to generate a temperature stabilized regulated voltage of about 3.2 volts. Except for the voltage reference device or circuit, the circuits of Figures 1 and 2 are essentially 50 identical. The same components in the circuits of the two figures are denoted by the same reference numerals. A description of the embodiment of Figure 2 will be limited to the reference circuit for the band interval voltage.

The band interval voltage reference circuit of Figure 2 includes an NPN transistor 40, the collector of which is connected to the output terminal 12 and at the base of which a signal is applied 55 from a voltage divider consisting of resistors 41 connected in series between the output terminal 12 and ground 16. and 42. The emitter of transistor 40 is connected through resistors 45 and 46 to collectors of a pair of NPN transistors 43 and 44, respectively. The resistance values of the

Claims (10)

192891 4 resistors 45 and 46 may be uneven. The collector of transistor 43 is connected to the bases of transistors 43 and 44. The collector of transistor 44 is connected to the base of an NPN transistor 47 whose collector is connected to the base of the pass transistor 13 and whose emitter is earth 16 is connected. The emitter of transistor 43 is directly connected to ground 16 and the emitter of transistor 44 is directly connected to ground 16 via a resistor 48. Transistors 43 and 44 and resistor 48 together form a logarithmic current source. In operation, the voltage at the base of transistor 13 is determined by the state of transistor 47 which is in turn driven by transistor 40. The voltage at the base of transistor 40 is a temperature-stabilized reference voltage that is equal to the sum of the 10 base-emitter voltage drops from transistors 40 and 47 and the voltage drop across resistor 46. The current through resistor 46 is determined by the logarithmic power source. Therefore, the voltage across resistor 46 heals a positive temperature coefficient that compensates for the negative temperature coefficients of the base-emitter junctions of transistors 40 and 47. The voltage divider consisting of resistors 41 and 42 provides an adjustment of the reference voltage. In the circuit of Figure 2, the band interval reference provides a lower regulated voltage than the Zener diode 15 in Figure 1. The diode 15 in Figure 2 serves to protect against arbitrary excessive positive voltage transients that are too fast for an adequate response by the band interval reference voltage. According to the above-mentioned explanation, the integrated circuit voltage regulator according to the invention is characterized by a considerably higher breakdown limit than with the known integrated circuit regulators. The control is not lost until the breakdown limit is exceeded. In the case of transistor breakdown, the internal circuit impedances continue to limit the current through the regulator so that it remains undamaged under all likely conditions to be expected. 25 1. Voltage control circuit comprising a first and a second opposite conductor type transistor connected in series with their collector-emitter circuit between a voltage source and a regulated output; a zener diode; a first base driving circuit for supplying a base voltage to the base of the first transistor connected to the output; and a second basic control circuit which is adapted to supply a base voltage to the base of the second transistor connected to the voltage source and which comprises a pre-control circuit forming part of the first basic control circuit which receives a feedback signal from the regulated output 35 characterized in that a current limiting element (21) is arranged in series with the series connection of the two transistors (13, 20); that a diode (22) is present between a reference voltage (16) and the junction of both transistors (13, 20); that the two basic control circuits (15.17; 23-27) supply constant basic voltages during operation; and in that the first basic driving circuit (15, 17) comprises the zener diode (15), which is included in the basic circuit of the first transistor (13) and which is part of one of the first basic driving circuit (15, 17). bias circuit (17) is set in forward direction. A voltage control circuit according to claim 1, wherein the controlled voltage at the output is positive relative to the reference voltage, wherein the first transistor is of the NPN type and the second transistor is of the PNP type, and wherein the emitter of the first transistor the output forms, characterized in that the current-limiting element (21) is arranged between the emitter of the second transistor (20) and the supply voltage source (11); and that the diode (22) is connected with its cathode to the junction of both transistors (13,20) and with its anode to the reference voltage (16). Voltage control circuit according to claim 2, characterized in that the current limiting element (21) is a P-type conductivity resistor which is diffused into an electrically insulated N-type 50 conductivity well. Voltage control circuit according to claim 3, wherein the second basic driving circuit comprises a field-effect transistor connected to the second transistor, characterized in that the second basic driving circuit comprises a first current mirror (24, 25) with a first, a second and a third terminal, which current mirror (24, 25) at a current of a predetermined size at the second terminal 55 produces a current of a proportional magnitude to the third terminal and the first terminal of which is connected to the reference voltage (16), and a resistor (26) between the output (12) and the second terminal of the first current mirror (24, 25); and that the field effect transistor (23) with its drain source circuit is included between the base of the second transistor (20) and the third terminal of the first current mirror (24, 25) and with its control electrode at the reference voltage (16) is connected. Voltage control circuit according to claim 4, characterized in that the biasing circuit (17) is provided with a third and a fourth transistor (36, 35) of the NPN type conductivity, the collector of the third transistor (36) having the base of the fourth transistor (35), the emitter of the fourth transistor (35) is connected to the base of the third transistor (36), and the emitter of the third transistor (36) is connected to the reference voltage (16); a resistor (37) connecting the base of the third transistor (36) and the emitter of the fourth transistor (35) to the reference voltage (16); a second current mirror (30, 10 31) having a first, a second and a third terminal which produces a proportional current at the third terminal at a current of a predetermined size at the second terminal; a resistor (32) between the supply voltage source (11) and the first terminal of the second current mirror (30, 31); a second and a third field effect transistor (33, 34) whose gate electrodes are connected to the reference voltage (16), whose drain electrodes are connected to the second terminal of the second current mirror (30, 31) and whose source electrodes are connected to the collectors of the third and fourth transistors (36, 35) are connected, and a connection of the third terminal of the second current mirror (30, 31) to the base of the first transistor (13) and to the cathode of the zener diode (15). Voltage control circuit according to claim 5, characterized in that the resistor (32) between the supply voltage source (11) and the first terminal of the second current mirror (30, 31) is a P-type conductivity resistor which is in a electrically insulated well of N-type conductivity is diffused. Voltage control circuit according to claim 6, characterized in that the zener diode of the first basic control circuit (15, 17) is connected between the base of the first transistor (13) and the reference voltage (16). Voltage control circuit according to claim 7, characterized in that the first basic driving circuit further comprises a reference voltage source comprising: a fifth transistor (47) of the NPN type conductivity, the collector of which is connected to the base of the first transistor (13) and whose emitter is connected to the reference voltage (16); a logarithmic current source (43, 44, 48) with a first, a second, a third and a fourth connection, which produces a current of an unambiguously involved size on the fourth connection with a current of a first size at the third connection, wherein the fourth terminal is connected to the base of the fifth transistor (47); a resistor (48) for connecting the first and second terminals of the logarithmic current source to the reference voltage (16); a sixth NPN type conductivity transistor (40) whose collector is connected to the emitter 35 of the first transistor (13) and whose emitter is connected through resistors (45, 46) to the third and fourth terminals of the logarithmic current source (43, 44, 48) is connected; and a third base driving circuit (41, 42) for supplying a substantially constant voltage to the base of the sixth transistor (40). Voltage control circuit according to any one of claims 6, 7 or 8, characterized in that the second 40 basic control circuit further has a fourth field effect transistor (27), the drain of which with the base of the second transistor (20) and whose source electrode and the gate electrode is connected to the reference voltage (16). Voltage control circuit according to claim 9, characterized in that the third basic control circuit consists of a voltage divider (41, 42) between the output (12) and the reference voltage (16). Hereby 1 sheet drawing